Follow-up and pressure fluid type servomotor



Feb., 7; 119@ L. H. BAGHLJISV 2,496,135@

FOLLOW-UP AND PRESSURE FLUID TYPE SERVOMOTOR Filed am.- 29, 1945 2sheets-sheet 1 F563 lin/2U @1Q/wf Feb. 7, 31%@ L.. H. BAGHUIS FOLLOW-UPAND PRESSURE FLUID TYPE SERVOMOTOR 2 Sheets-Sheet 2 Filed Oct. 29, 1945FIEL7 FIGB FIGS

zz/v e @i010 Patented Feb. 7, 195() UNITED STATES PATENT OFFICEf2;4'9s,369 F rontowmrnnniaifmssinn Fiom .'rYiiE c sERvoMoToR Luanne-usHiiafikus Beginns, Utrecht, Netherlands Aspiissfioiijoc'fote* s Claiis.v'(01. 121411) The invention relates to mecl'ianismifortra'ns''- formingrotary motion into 'rectilinear motion with the air of a hydraulic or apneumatic motor, andparticularly to auxiliary 'steering mechanism for.motor vehicles comprising' "on the one hand a pair of elementsconsisting of a cylinger'and piston, and on the otherhand a pair orelements consisting of a screw spindle and anut, one element of the rstmentioned Ypair (preferably the cylinder) beingstationary and .the`otherjtplref erably the piston) -being adapted for rectilinearmovement, locked against rotation 'and coiiple'd with one element(preferably the nut) of tire latter pair, the other .element of vvhlch(preji erably the screw spindle) being adaptedifojrota tion, whereas,with a view to' the actuation of lift valves for the supply ofpressur'euid "to the discharge thereof from 'the'eyli'nder spaces'situated on both sides of the piston, nrs rotatable element (the screwspindle) is adapted to freely rotate through a certain angle beforetherectiflinearly movable element (the piston) lis aetnated.

In known devices of this kind, ,the valves are mounted within the piston-and actuated as' a consequence of the relative movement ofthe niit andthe piston. To that end, these elements are' interconnected with acertain amointof ,play. These devices must 'be provided with long'pis'-tons and cylinders. v y

, In other known mechanism for the sainepurpose. the valves are mountedoutside the lcylinder and the piston andconnected to the'latteij bymeans of an independent screw Spindler and nut. In consequencethereo'f,`the lengths f the cylinder and the piston may be small.

The present invention differs from tne'known devices in this, that oneelement (preferably the nut) of the pair consisting of screw spindle nutis integral with'or attached witlioutplay' to the rectilinearly movableelement (for instance the piston), and that'the rotatable element (forinstance the screw spindle .is adapted tomve axially, the stroke thereofbeingbonined tween abutments. Mechanism in accordance'witn the inventionhas the 'advantage 'that Icorni prises only one single screw `spindle'aiidnutyislrajt the lift Valves may be mounted `outsiif'e;thepislf tonand the cylinder, and that'the'piston andthe cylinder may have smalldimensions injaxial `direction. Furthermore, it is very 'compact andcannot easily be damaged.

According to theinve'ntion, 'all valves `Qfor the distribution of thepressure uid may bemountd on 'the rotatable element (preferably thescrew spindle) and be closed and opened by the axial movement of saidelement. It is also possible for only a part of the number of valvesbeing mounted on 'the rotatable element and actuated bythe axialmovement thereof, and 'for the other valve's'being connected to saidelement by a friction ooupling 'and operated as a consequence of therotation of ,that element.

"Referring to the drawings, which, by way of example only, snow severalembodiments of the invention: l

Fig. 1 is afdiagrammatic'longitudinal sectional View o'f ahydralicsteering mechanism for a motor vehicle,V p

2 is a detailed sectional view on an enlarged scale of a portion of themechanism accoming to' Fig. -1,

Fig. V3, is a cross section of theline III-III of Fis. 2.

Fig. 4 is a cross section of the line IV-IV of Fg.'2,

Fig'. l5 isa longitudinal sectional View of a second embodiment of theinvention,

6 shows a detail of the mechanism according to'Fig'. 5 on an enlargedscale, and

Figf'is acrossv section on the'line VII-VII, of Eis'. c.

'In Figs. 'i`4, designates a cylinder and 2 is a piston of aservo'motor. The piston 2 is rigidly attaehed to a piston rod 3, whichat its free end (not shown) jis adapted to be connected to the systernto be' steered, e. g., to the steerable wheels of 'a motor vehicle. Thepiston rod is provided with akey'preventing rotation 'of the piston 2.Mounted in the vcenter line of the piston rod 3 vis a screw spindle'5,'coopeijating with a corresponding'thregaded boret 'of the piston 2.The screw spindle 'Bis' supportedfor rotation and for axialdisplaeement'bythe cylindercover 'l and adapted to be'rotatedby'means ofa ro'd', for instance the steering'r'od of `aimotofr vehicle; TheVsteeringv rod 8 'and-the screw spindle 5 are interconnectedby'bevelgear wheels 9 and HJ, the'lwheel -I0 being' mounted fory'sliding movement on the plain portion of-tne screw spindle. A'partition lil sepa* rates a chamber f2 in the cylinderhead from theother cylinder spaces, 'said chamber comlmunicating with the cylinder`spaces M and fili and with a-valvebox I8 through yanl aperture I3 insaid partition H, through a conduit l5 and through a conduitl1,'respectively. 'Theaperture' t3 can :be closed by vmeans-'of liftvalves 'I9 fand ZUmountedfon-thescrew spindle 5. 'Saidcspndle' 3 has anaxial bore 2I opening through a cross bore 22 into the space between thevalves I9 and 20 and serving as a discharge passage for the pressurefluid, e. g. oil. The supply of pressure uid from a pump (not shown) iselected through a conduit 23 connected to the valve box I8. Moreover,said box communicates with the cylinderspace I4 through a conduit 24.Mounted within the valve box I8 is a double acting valve 25 of the lifttype controlling the passageof pressure fluid from the supply conduit 23to one or the other of the conduits II or 24. The valve is moved fromone position to the other depending upon the direction in which thescrew spindle is rotated by a spring 21 coiled in frictional contactwith the screw spindle and having the end 26 extended and connected withthe stem of the valve 25 coupled with the screw spindle by means of afriction coupling 26, 21 (Fig. 3) and actuated when said spindle isrotated. Encircling the spindle 5 is a spring 28 counteracting rotationof the screw spindle from the position shown in Fig. l, in whichposition the piston is about in the'middle of the cylinder, said springbeing strong enough to return the screw spindle to its neutral positionafter the steering wheel-has been released. If the hydraulic deviceoperates properly, a force just suicient to overcome the friction of thescrew spindle and of the steering rod will do for returning said spindleto its neutral position.

The apparatus operates as `follows:

If the steering rod 8 is rotated in clockwise direction, the screwspindle 5 rotates in counterclockwise direction and will move toward theleft, since it is screwed out of the piston 2 held by the load to bedisplaced. Owing to this rotation of the screw spindle 5, valve 25 ismoved into the position shown in Figs. l-3 by the pull exerted thereonby the spring of the friction coupling 26, 2l thus closing conduit I'I.Due to the axial displacement of the screw spindle 5, the aperture I3 inpartition I I is closed by valve 20. In this position of the valves 2]and 25, pressure fluid which continuously ilows through the hydraulicsystem during the .steering operation, is supplied to the cylinder spaceI4 through conduit 23, valve box I8 and conduit 24, and fluid can bedischarged from the cylinder space I6 through conduit I5, chamber I2,cross bore 22 and axial bore or passage 2I to the suction side of thefluid pressure pump (not shown). The piston is thereby moved to theright and the load is displaced. When the steering wheel is not turnedfurther, the piston and the screw spindle are moved in unison to theright by the pressure of the fluid, and owing to the valve 20 beingopened the cylinder space I4 is put in communication with the dischargeconduit 22, 2| so as to relieve the piston of pressure. If, however,rotation of the screw spindle in the chosen direction is continued, thevalves remain in the position shown and the displacement of the pistondue to the pressure of the uid continues corresponding to the rotationand the pitch of the screw spindle. It will be apparent that eachposition of the screw spindle or of the steering rod corresponds to adefinite position of the piston.

If the described device is used as a steering mechanism for a motorvehicle, it is desirable that, after the steering wheel has beenreleased, the wheels of the vehicle automatically return to theirneutral position.

This, however, is wnot possible without the aid of special means, sincetravel of the piston is only possible during rotation of the screwspindle. To this end, a spring 28 is provided for counteracting therotation of the screw spindle from its neutral position.

As soon as the steering wheel has been released, saidspring returns thescrew-spindle toA its neutral position. During the return movement,valve is moved to its other position in which the supply conduit 23,instead of being connected to conduit 24, is connected to conduit I'I.This movement of the valve 25 is caused by the slackening of the coilsof the spring 21 and the resulting thrust .imparted to the end 26 andthe valve 25. Simultaneously, valve I9 is closed and valve 20 opened.The cylinder space I6 is thereby lled with pressure fluid, and fluid canbe discharged from the cylinder space I4. The piston is thus returned toits center position. If the screw spindle is rotated in the oppositedirection, conditions will be reversed.

It is apparent that there is a certain amount of play between themovement of the screw ton (the front wheels of the vehicle). This playis necessary for the operation of the valves and need not be larger thanthat existing in ordinary mechanical steering devices, so that it willnot aiect the steering operation.

If the hydraulic or pneumatic part of the mechanism does not operateproperly, for instance, if no uid pressure is available, the piston andthe parts connected thereto can be operf ated manually. During rotationof the screw spindle, the total force required for the steeringoperation must then be exerted on the piston by the thread o f the screwspindle. Since in this case said force is not furnished by the pressurefluid, the steering operation requires much more energy than when thehydraulic or pneumatic system is in operation. In order to take up thereaction forces exerted on the screw spindle, valves I9 and 20 areconstituted as thrust bearings (Fig. 2). When the described hydraulicdevice is in operation, the force required for steering has only to besuflicient to overcome the friction of the screw spindle, that of thesteering rod and the force of the spring 28, so that steering isextraordinarily light.

In Fig. 2, the valve seat connected to conduit 24 is formed on a screwplug 29 screwed in the valve box. The lift of valve 25 can be adjustedby means of the screw plug 29.

It is observed that the described devices are not conned to their use insteering mechanisms for motor vehicles. Many other forms of details arepossible within the scope of the invention. For instance, the screwspindle and the nut, or the piston and the cylinder, may beinterchanged.

In the straight position of the steerable front wheels of the vehicle,the piston 2 is practically unloaded in the middle of the cylinder I andneither valve I9, nor valve 2D is closed, causing a continuous ow offluid from the pressure conduit 23 into the suction conduit 2I andbringing about a loss of energy. In order to avoid these losses in themechanism according to Fig. 5, the bores 22 are closed by a slide valve48 mounted within the axial bore 2I when the piston 2 is in its neutralor center position. This slide valve is connected to the piston rod 3and thus to the piston 2 by means of a rod 49. Assuming the steeringwheel or the screw spindle 5 to be rotated, said spindle is axiallymoved with respect to the piston, the discharge bores 22 are opened, oneof the valves I9, 20 is closed and pressure fluid is admitted on oneside of the piston. The slide valve 48 is hollow (Figs. 6 and 7), sothat, after downward displacement thereof (Fig. 5) and after opening ofthe bores 22, the fluid can iiow into the discharge conduit 2| throughthe slide valve.

What I claim is:

1. An apparatus for transforming rotary motion into rectilinear motionwith the aid of hydraulic or pneumatic means, in particular an auxiliarysteering mechanism for motor vehicles comprising in combination a.cylinder and a piston forming one pair of cooperating elements, oneelement of which being stationary and the other being locked againstrotation and adapted for rectilinear displacement, a screw spindle and anut forming a second pair of cooperating elements, one element of whichbeing attached without play to the rectilinearly displaceable element ofthe first mentioned pair of elements and the other being adapted forrotation and restricted axial movement and capable oi rotating freelythrough a certain angle before actuating the rectilinearly displaceableelement, cylinder spaces situated on both sides of the piston, andpoppet valves for the supply of pressure fluid to and discharge thereoffrom said cylinder spaces, and consisting of movable valve discs andstationary seats, said valves being adjusted by and during the freerotation of said rotatable element and the valve discs of at least partof the number of valves being mounted on said rotatable element andadapted to be closed and opened by the slight axial displacement of saidrotatable element, said mounted valve discs and cooperating with theirrespective stationary seats and constituting abutments to confine axialdisplacement of said rotatable element.

2. An apparatus as claimed in claim l, in which part of the number ofvalve discs are mounted on said rotatable element and the remainingvalves are adapted to be closed and opened as a consequence of therotation of said element.

3. An apparatus as claimed in claim 1, comprising a slide valveconnected to the rectilinearly displaceable element and adapted to closethe pressure fluid discharge conduit when said element is in its centerposition.

LUDOVICUS HENDRIKUS BAGHUIS.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,500,685 Roberts July 8, 19241,651,838 Roberts Dec. 6, 1927 2,213,271 Davis Sept. 3, 1940 2,237,400Washburn Apr. 8, 1941

